全文获取类型
收费全文 | 91532篇 |
免费 | 1915篇 |
国内免费 | 288篇 |
专业分类
化学 | 49245篇 |
晶体学 | 623篇 |
力学 | 2481篇 |
综合类 | 13篇 |
数学 | 20172篇 |
物理学 | 21201篇 |
出版年
2023年 | 470篇 |
2022年 | 378篇 |
2021年 | 677篇 |
2020年 | 944篇 |
2019年 | 895篇 |
2018年 | 2438篇 |
2017年 | 2538篇 |
2016年 | 3029篇 |
2015年 | 2409篇 |
2014年 | 2306篇 |
2013年 | 4795篇 |
2012年 | 6880篇 |
2011年 | 6220篇 |
2010年 | 4170篇 |
2009年 | 3522篇 |
2008年 | 4131篇 |
2007年 | 3969篇 |
2006年 | 3585篇 |
2005年 | 7080篇 |
2004年 | 6126篇 |
2003年 | 4129篇 |
2002年 | 2184篇 |
2001年 | 1598篇 |
2000年 | 1378篇 |
1999年 | 1064篇 |
1998年 | 784篇 |
1997年 | 643篇 |
1996年 | 829篇 |
1995年 | 585篇 |
1994年 | 672篇 |
1993年 | 648篇 |
1992年 | 778篇 |
1991年 | 623篇 |
1990年 | 651篇 |
1989年 | 540篇 |
1988年 | 531篇 |
1987年 | 455篇 |
1986年 | 427篇 |
1985年 | 587篇 |
1984年 | 538篇 |
1983年 | 426篇 |
1982年 | 410篇 |
1981年 | 413篇 |
1980年 | 352篇 |
1979年 | 367篇 |
1978年 | 352篇 |
1977年 | 333篇 |
1976年 | 392篇 |
1974年 | 329篇 |
1973年 | 361篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Márton Kiss 《Acta Mathematica Hungarica》2006,110(3):253-259
Summary New results for the eigenvalue ratios of vibrating strings are presented partially in connection with previous results concerning
Schr?dinger operators. 相似文献
52.
In this note we study uncertainty sequencing situations, i.e., one-machine sequencing situations in which no initial order
is specified. We associate cooperative games with these sequencing situations, study their core, and provide links with the
classic sequencing games introduced by Curiel et al. (Eur J Oper Res 40:344–351, 1989). Moreover, we propose and characterize
two simple cost allocation rules for uncertainty sequencing situations with equal processing times. 相似文献
53.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献
54.
N. Hegyvári 《Acta Mathematica Hungarica》1989,53(1-2):149-154
55.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure,
over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative
measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique
of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained
quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely
different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms
of cyclic coarse-grained quantum logics. 相似文献
56.
57.
Piotr Ko?cielniak 《Topology and its Applications》2007,154(9):1951-1955
Let M be a compact manifold with dimM?2. We prove that some iteration of the generic homeomorphism on M is semiconjugated to the shift map and has infinite topological entropy (Theorem 1.1). 相似文献
58.
We study the spectral properties of a large class of compact flat Riemannian manifolds of dimension 4, namely, those whose
corresponding Bieberbach groups have the canonical lattice as translation lattice. By using the explicit expression of the
heat trace of the Laplacian acting on p-forms, we determine all p-isospectral and L-isospectral pairs and we show that in this class of manifolds, isospectrality on functions and isospectrality on p-forms for all values of p are equivalent to each other. The list shows for any p, 1 ≤ p ≤ 3, many p-isospectral pairs that are not isospectral on functions and have different lengths of closed geodesics. We also determine
all length isospectral pairs (i.e. with the same length multiplicities), showing that there are two weak length isospectral
pairs that are not length isospectral, and many pairs, p-isospectral for all p and not length isospectral.
Mathematics Subject Classifications (2000): 58J53, 58C22, 20H15. 相似文献
59.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
60.
Generally, in homotopy theory a cylinder object (or, its dual, a path object) is used to define homotopy between morphisms,
and a cone object is used to build exact sequences of homotopy groups. Here, an axiomatic theory based on a cone functor is
given. Suspension objects are associated to based objects and cofibrations, obtaining homotopy groups referred to an object
and relative to a cofibration, respectively. Exact sequences of these groups are built. Algebraic and particular examples
are given. We point out that the main results of this paper were already stated in [3], and the purpose of this article is
to give full details of the foregoing. 相似文献